Fix a bug in "hg" module so that `pull` is not set to a version.

There is a bug in the `hg` module where if a `tag` is used it won't
properly be able to update to it.

This problem is exhibited on repository where a tag is moved from an
older commit to a newer commit.
Merge branch 'devel' of https://github.com/calebbrown/ansible into calebbrown-devel